1. Field of the Invention
This invention relates to turbine-based devices, such as windmills and water turbines, for transforming the motion of fluids into useable mechanical energy. More particularly, this invention relates to an improvement in such devices having a reaction surface feathering cycle related to the direction of fluid motion.
2. Description of the Related Art
The use of devices for obtaining useful energy from the motion of fluids in nature dates from antiquity. Such devices have long been employed to mill grain, pump water, saw lumber and provide other forms of mechanical energy. In recent times, as awareness has increased of the finite nature of fossil fuel sources, as well as of the deleterious environmental consequences of their use, devices driven by natural forces have attracted interest as sources of clean energy that are not subject to depletion. Employment of such devices presents the prospect of abundant energy production, not only directly for use in an energy grid by coupling the mechanical output of such devices to electrical generators, but also as generators of stored energy in the form of charged fuel cells or directly useable electrolytically produced hydrogen gas.
Of devices transforming fluid motion into useable mechanical energy, those devices, such as windmills and water wheels, which employ turbine mechanisms to transform fluid motion into mechanical rotation are perhaps the best known. Mechanically, such turbine-based devices may be regarded as falling into two broad categories.
One category of turbine-based device, in its operative state, presents the axis of turbine rotation substantially parallel to the direction of fluid flow. The classic western American water windmill is exemplary of devices in this category. Impellers for such devices are designed and disposed so as to optimize the angular momentum of the turbine assembly when the turbine faces the fluid flow with the axis of turbine rotation substantially in line with the direction of flow. To provide for changing flow direction, such devices typically orient the turbine in relation to fluid flow by providing a means for rotatably orienting the device about an orientation axis, the orientation axis orthogonal to the axis of turbine rotation, whereby, for optimal momentum, the axis of rotation may be oriented so as to be in line with fluid flow as flow direction changes. Elaborations on this technology, such as U.S. Pat. No. 97,136 to Tustin, adjustably orient the axis of turbine rotation out of line with the fluid, intentionally limiting efficiency of the turbine to conserve water, for example. In any case, though, because they require movement of the turbine rotation axis about an orientation axis, turbines in this category typically require additional mechanical complexity, such as differential gearing, to accommodate such movement, thereby increasing the cost and diminishing the reliability of the turbine assembly. Turbines in this category also require additional space within which to operate so that they may oriented at various times for proper alignment as flow direction changes. Because of the foregoing problems, turbines in this category are not easily adapted to large-scale operations.
Another category of turbine-base device, in its operative state, presents the axis of turbine rotation perpendicular to the plane of fluid flow. For such turbines, the orientation of the turbine axis is fixed. In the case of windmills in this category, the turbine axis is vertical.
As a turbine in this category rotates, some of its impellers will be heading in the direction of fluid flow (called “windward” herein) and some will be heading in the opposite direction (called “leeward” herein). The torque developed by such a turbine in response to fluid movement depends upon how the design of the turbine apparatus maximizes the motive effect of fluid movement on the impellers moving in the windward direction and minimizes the retarding effect of fluid movement on the impellers moving in the leeward direction.
Some turbines, such as that taught in U.S. Pat. No. 5,038,049 to Kato, employ structures or assemblies to direct fluid flow across one side of the turbine while the other side of the turbine is sheltered. Others, such as taught by Sara Jane Rollason in U.S. Pat. No. 529,197, orient a shield in response to flow direction to shelter the leeward side of the turbine. By such means, only impellers on the windward side receive motive force, and net torque is thereby imparted to the turbine. The efficiency of such devices is limited, however, because impellers on the leeward side of the turbine are nonetheless retarded by the resistance of their impeller aerodynamic profile in still fluid.
Some other turbines employ impellers which, by their design, present a low aerodynamic profile on one side and a high aerodynamic profile on the other side. For example, the turbine in U.S. Pat. No. 4,329,593 to Willmouth employs cup-like impellers in the manner of an anemometer. In such designs, the fluid resistance of the leeward tending side of the impellers, while less than that of the windward tending side, is great enough to limit turbine efficiency significantly. Yet other turbines along these lines employ airfoil type impellers, such as the Darrieus turbine, U.S. Pat. No. 1,835,018. For such impellers, fluid forces are divided into lift and drag forces, with a component of the lift force causing rotation and a component of the drag force opposing rotation. The driving torque will be positive as long as the driving component of the lift force exceeds the opposing component of the drag force. As is well appreciated by those of skill in the art, however, in systems employing Darrieus type turbines, the aerodynamic performance is poor at low wind speeds and the blades may stall at low rotational speeds. Consequently, some type of auxiliary device such as a motor must usually be employed to start the system.
To overcome these limitations in the art, various turbine designs have been employed wherein the impellers are “feathered” or moved in variable orientation, so as to be fully exposed to fluid pressure as the impellers rotate on the windward side of the turbine and to be almost entirely withdrawn from the fluid pressure as the impellers rotate on the leeward side of the turbine. In such a manner, the motive force on the windward impellers is maximized and the retarding force on the leeward impellers is minimized, thereby maximizing the torque produced by the apparatus.
For example, U.S. Pat. No. 584,986 to Chapman describes a windmill in which impellers are affixed to rotatable axes that are perpendicular to the axis of rotation of the turbine. The impellers are able to flap up from a vertical, fluid resisting position to a horizontal position lacking fluid resistance in one direction only, their movement in the opposing direction impeded by a projection integral to the panel that is engaged by a frame around the panel. Thus, impellers in Chapman are held vertical by engagement of the projection during the windward portion of their rotation and are pushed horizontal by fluid resistance on the leeward portion of their rotation. Turbines in more recent patents, such as U.S. Pat. No. 4,818,180 to Liu, employ similar fluid-driven feathering. A limitation of all such technologies is that the force necessary to cause the impellers to flap up also acts as a retarding force counteracting the motive force on the windward impellers, thereby limiting the efficiency of such turbines.
A modem approach to feathering impellers during rotation in order to maximize fluid resistance on windward impellers and minimize fluid resistance on leeward impellers is shown in U.S. Pat. No. 4,113,408 to Wurtz et al. In such turbines, impeller orientation is adjusted throughout turbine rotation by electrical or electro-mechanical means responsive to the direction of fluid flow. Thereby, impeller feathering may be optimized for maximum torque. A material limitation in this and related art, such as taught in U.S. Pat. No. 5,195,871 to Hsech-Pen, is that it relies on electro-mechanical components for operation, to the detriment of economy and reliability.
Purely mechanical feathering is arguably a more economical and reliable approach. For example, both U.S. Pat. No. 675,075 to Warren and U.S. Pat. No. 4,494,007 to Gaston employ a sprocket and chain mechanism coupled to a wind vane for controlling feathering orientation responsive to wind direction.
The turbine in U.S. Pat. No. 961,766 to Folger employs a weather vane controlled sprocket mechanism engaging all the impellers for feathering, while that in U.S. Pat. No. 955,305 to Bailey describes a feathering orientation mechanism based upon linkage between impeller axles and gearing coupling the orientation of one impeller axle with the orientation of a wind-vane.
Each of the forgoing mechanical feathering mechanisms relies on sprockets and/or chains for coordinating impeller feathering during turbine rotation. As is well known to those in the art, such mechanisms present measurable friction, impeding motion and reducing efficiency, and may be subject to failure, particularly at higher rates of turbine rotation.
Among mechanical feathering assemblies, those employing offset cam mechanics may offer less friction and greater reliability in operation than other alternatives. For example, U.S. Pat. No. 591,775 to Peterson employs an annular eccentric frame acting in the manner of an offset cam on cantilevered journals from the impellers. In Peterson, feathering is oriented according to wind direction by way of a geared linkage between a wind-vane and the annular eccentric frame, whereby the direction of eccentricity of the frame may be varied according to wind direction, thereby controlling the orientation of feathering.
U.S. Pat. No. 618,807 to Staplin et al. describes a wind engine comprising vertically oriented trough-like impellers, with feathering achieved by engagement of a spring-biased arm mechanism from the shaft or axle of each impeller with an eccentric annular groove in a sleeve around the axis of the turbine. The orientation of the sleeve (and thereby the orientation of the eccentricity of the groove in the sleeve) is determined by the orientation of a wind-vane that is directly affixed to the sleeve. The arms following the eccentric groove are displaced by that amount necessary to achieve appropriate feathering as the impellers rotate about the sleeve.
U.S. Pat. No. 4,218,184 to McPherson et al. describes windmill construction with two modes of feathering for two distinct purposes. The first mode of feathering, not highly relevant to the present invention, moves all of the impellers parallel to wind direction, for the purpose of braking the turbine mechanism. McPherson's second mode of feathering, though, comprises following the elliptical perimeter of a cardioid cam with a roller bearing on a spring-biased rocker arm operatively coupled to the impellers, thereby varying impeller orientation with turbine rotation to achieve appropriate feathering for maximizing torque.
While Staplin and MacPherson both employ a cam mechanism that may be superior to other means of feathering in efficiency and reliability, both suffer from the limitation of requiring a spring-biased mechanism with roller to follow the cam. As is well-known to those in the art, such mechanisms require periodic maintenance, such as replacement of broken or worn-out springs.
It is an object of the present invention to provide an improved fluid driven turbine with impeller feathering that maximizes torque derived from fluid flow.
It is a further object of this invention to provide a fluid driven turbine with impeller feathering that is efficient even at low fluid flow velocities.
It is a further object of this invention to provide mechanics for feathering impellers in a fluid driven turbine that are responsive to fluid flow direction.
It is a further object of this invention to provide mechanics for feathering impellers that do not rely on spring-biased mechanisms.
It is a further object of this invention to provide mechanics for feathering impellers that are reliable and efficient.